Materials that exhibit low friction are needed in a variety of applications such as bearings, seals and the like. Composites of nickel oxide and calcium fluoride or zinc oxide, stannous oxide and calcium fluoride are currently under investigation for use in low friction applications. These materials have friction coefficients of approximately 0.6 and service lives of only 500 hours. There is therefore a need to develop materials that exhibit the characteristics of a low coefficient or friction, low wear, and high temperature operating capabilities. Conventional materials such as those comprised of carbon generally have good tribological properties at low temperatures, but tend to become easily graphitized and lose their low coefficient of friction at higher temperatures.
Carbon/carbon composites in which a carbon matrix is reinforced with carbon fiber is one form of these conventional carbon materials. The initial use of these materials was in providing thermal barriers in aerospace vehicles. Such applications are based on the very high temperature capability, i.e., at temperatures up to 5400.degree. F. (3000.degree. C.), of these carbon/carbon composites. At the present time, the major use of carbon/carbon composites is in aircraft brakes with approximately 85% of total carbon carbon/composite production targeted toward this market sector. Previously known properties of carbon/carbon composites which make them an ideal candidate for aircraft brakes are: (1) high coefficient of friction (in the range of 0.4-0.5); (2) high temperature capability; and (3) low weight.
The present inventors have developed a novel use and application for modified carbon/carbon composite materials, which makes use of heretofore unknown characteristics of a specialized class of carbon-carbon materials in applications requiring very low friction and very high wear resistance. These characteristics, coupled with the high temperature capability of the carbon/carbon composite, make this material particularly adapted for use in applications such as bearings, seals and virtually any component or element which engages another body in a frictional manner.